Ocular histoplasmosis in man has remained an enigma since the cause and effect of this clinical entity has not yet been clearly established. Up until recently experimentation has shed limited information concerning the nature of this visually disabling disorder. Lately, evidence has been brought forth to show that when rabbits were infected systemically with the spore form of a naturally occurring strain of Histoplasma capsulatum, formation of multiple discrete granulomas were found in the choroid of these experimental animals. Ophthalmologically, these resolved lesions appear similar or identical to those miliary punched out lesions observed in man. In contrast, the yeast phase of the same strain of fungus failed to produce similar lesions of the eye. Organisms which could be identified microscopically as H. capsulatum were seen only in those eyes removed for examination soon after the appearance of uveitis. Similar studies have not yet been reported with the use of primates. Experimentation in the latter animal species is logical and imperative in view of the close similarities of the ocular anatomy in monkey and man. Significantly, there remains the necessity to reproduce the hemorrhagic disciform lesion of the macula which represents the gravest aspect of presumed ocular histoplasmosis. The objectives and methods of this project are: 1) to produce ocular lesions in primates similar to those seen in presumed ocular histoplasmosis through systemic fungus infection with Histoplasma capsulatum; 2) to determine the relationship between the onset of the ocular pathology and the development of antibody and cellular immunity to histoplasmosis; 3) to attempt to fulfill Koch's postulates; 4) to develop effective means of therapy and possible measures of prevention through the refinement of a vaccine.